Auditory facilitation in deterministic versus stochastic worlds.

The brain learns statistical regularities in sensory sequences, enhancing behavioral performance for predictable stimuli while impairing behavioral performance for unpredictable stimuli. While previous research has shown that violations of non-informative regularities hinder task performance, it remains unclear whether predictable but task-irrelevant structures can facilitate performance. In a tone duration discrimination task, we manipulated the task-irrelevant pitch dimension by varying transition probabilities (TP) between successive tone frequencies. Participants judged duration, while pitch sequences were either deterministic (a rule-governed pitch pattern, TP = 1) or stochastic (no discernible pitch pattern, TP = 1/number of pitch levels). The tone pitch was task-irrelevant and it did not predict duration. Results showed that reaction times (RTs) were significantly faster for deterministic sequences, suggesting that predictability in a task-irrelevant dimension still facilitates task performance. RTs were also faster in two-tone sequences compared to eight-tone sequences, likely due to reduced memory load. These findings suggest that statistical learning benefits extend beyond task-relevant dimensions, supporting a predictive coding framework in which the brain integrates predictable sensory input to optimize cognitive processing.